tmp colors

.config/gnome-settings/derive-palette.py

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+"""Derive a full color palette from a GNOME accent.
+
+The palette is a single-hue ramp of 7 stops in OKLCH:
+ - All stops share the anchor's hue
+ - Lightness descends in uniform steps, with the anchor centered
+   => Choosing the light end also determines the dark end by mirroring
+ - Chroma follows a bell over lightness, peaking at the anchor
+
+In addition, 5 accent hues with 2 shades each are derived
+for the terminals' ANSI colors.
+
+The resulting values are recorded in the palette table in ./README.md
+and this script is the source of truth for all colors.
+
+Usage: `python3 derive-palette.py`
+       (requires `pip install coloraide` before)
+"""
+
+import coloraide
+
+ANCHOR = "#2190A4"  # GNOME's teal (i.e., libadwaita's "--accent-teal")
+
+L_LIGHT = 0.933  # The one chosen parameter
+
+# Tail values of the chroma bell at the ramp's two ends
+# where the dark tail is held high enough to keep the darkest stop
+# appear in the chosen accent's hue
+C_LIGHT, C_DARK = 0.017, 0.055
+
+# Canonical hue angles (in OKLCH)
+# for the terminal's semantic colors
+ACCENT_HUES = {
+    "red": 25,
+    "yellow": 95,
+    "green": 145,
+    "blue": 260,
+    "magenta": 330,
+}
+
+# The anchor's lightness, chroma, and hue seed everything below
+a = coloraide.Color(ANCHOR).convert("oklch")
+AL, AC, H = a["lightness"], a["chroma"], a["hue"]
+step = (L_LIGHT - AL) / 3
+
+
+def hexify(L, C, h=H):
+    """Convert an OKLCH color to an upper-case sRGB hex string.
+
+    Colors outside the sRGB gamut are fitted by reducing chroma
+    while preserving lightness and hue; in this palette that only
+    affects the darkest stops, where sRGB cannot hold the full chroma.
+    """
+    return (
+        coloraide.Color("oklch", [L, C, h])
+        .convert("srgb")
+        .fit(method="oklch-chroma")
+        .to_string(hex=True, upper=True)
+    )
+
+
+def bell(L):
+    """Return the ramp's chroma at lightness `L`.
+
+    Chroma follows a parabola over lightness: it peaks at the anchor
+    (i.e., `AC`) and falls off to `C_LIGHT` at the light end and `C_DARK`
+    at the dark end of the ramp. So, both ends still appear in the chosen
+    accent's hue without ever exceeding the anchor's saturation.
+    """
+    end = C_LIGHT if L >= AL else C_DARK
+    t = (L - AL) / (3 * step)
+    return AC - (AC - end) * t * t
+
+
+def lift(h):
+    """Return the lightness at which hue `h` reads on the dark base.
+
+    Starting from the anchor's lightness, raise it in steps of 0.01
+    until the color reaches a WCAG 2.1 contrast of 4.5:1 against the
+    ramp's darkest stop (i.e., `dark_base`, defined below but before
+    the first call). The accents' lightness is thereby solved
+    from the contrast requirement rather than chosen by hand.
+    """
+    L = AL
+
+    while (
+        coloraide.Color(hexify(L, AC, h)).contrast(
+            dark_base,
+            method="wcag21",
+        )
+        < 4.5
+    ):
+        L += 0.01
+
+    return L
+
+
+ramp = [
+    hexify(AL + k * step, AC if k == 0 else bell(AL + k * step))
+    for k in range(3, -4, -1)
+]
+
+dark_base = coloraide.Color(ramp[-1])
+
+
+accents = {}
+
+for n, h in ACCENT_HUES.items():
+    L = lift(h)  # Solve only once per hue
+    accents[n] = (
+        hexify(L, AC, h),
+        hexify(L + 0.10, AC, h),
+    )
+
+
+print("ramp:", *ramp)
+
+for n, (norm, bright) in accents.items():
+
+    print(f"{n}: {norm} {bright}")